1. Field of the Invention
The invention relates to a lane marker recognition apparatus and a lane marker recognition method executed by that apparatus. More particularly, the invention relates to a lane marker recognition apparatus provided in a movable object such as a vehicle, and a lane marker recognition method executed by that apparatus.
2. Description of the Related Art
Vehicles are known which are provided with any of a variety of assist systems such as a lane departure warning system which determines that there is a danger of lane departure while traveling when the distance to a lane marker of the lane in which the vehicle is traveling becomes equal to or less than a predetermined threshold value, and notifies the driver of that danger, and a preventive safety system that automatically takes up the slack in a seatbelt and automatically activates a brake when a numerical value based on the relative position and relative speed between the vehicle and an object (such as another vehicle or a pedestrian or the like) detected by laser becomes equal to or less than a predetermined threshold value. One example of such an assist system is the lane departure prevention system described in Japanese Patent Application Publication No. 2001-206237 (JP-A-2001-206237).
The system described in JP-A-2001-206237 performs a lane change determining process in which it determines whether the steering torque and/or the lateral offset from the center in the width direction of the lane has exceeded a respective predetermined threshold value, and determines that the vehicle will change lanes if the threshold value has been exceeded. If it is determined that the vehicle will not change lanes, lane keeping control is performed by generating a normal amount of steering torque so that the vehicle travels in the center of the lane. Meanwhile, with the system described in JP-A-2001-206237, when it is determined that the vehicle will cross a lane marker of the lane and change lanes, a change type determining process starts to be performed in which the system determines whether the change is a road change in which the lane marker that the vehicle is attempting to cross is a solid line, or a lane change in which the lane marker that the vehicle is attempting to cross is a broken line, based on the results from a processed image of the road surface in the direction in which the vehicle is traveling.
Here, a solid lane marker is used for separating a road from a sidewalk by a solid white line, for example, and a broken lane marker is used for separating the lanes on a two or three lane road by a white broken line, for example. Therefore, when the vehicle is attempting to cross a solid lane marker, it can be assumed that the vehicle is veering off of the road onto the sidewalk. On the other hand, when the vehicle is attempting to cross a broken lane marker, it can be assumed that the vehicle is making a normal lane change in which the vehicle is changing from one lane to an adjacent lane. Incidentally, a road change may be considered to be a highly significant lane change for the driver.
Therefore, with the system described in JP-A-2001-206237, when the change type determining process starts and it is determined that the vehicle is attempting to cross a solid lane marker, it is determined that the vehicle is making a highly significant road change in which it is necessary to warn the driver, and the system performs a lane departure preventing operation in which it prevents the vehicle from veering off of the road by generating more steering torque than normal to make the vehicle travel in the center of the lane, i.e., by generating more steering torque than normal in the opposite direction of the steering torque generated by the driver which corresponds to the road changing direction. Accordingly, with the system described in JP-A-2001-206237, when the vehicle is making a highly significant road change, a lane departure preventing operation is performed which generates torque in the direction opposite the direction of the steering torque generated by the driver, which both prevents the vehicle from veering off of the road and makes the driver aware of the fact that the vehicle is making a highly significant road change.
However, the system described in JP-A-2001-206237 has the following problems. That is, as described above, when the steering torque and/or the lateral offset from the center of the lane exceeds the respective predetermined threshold value, it is determined that the vehicle is changing lanes so the change type determining process starts.
However, if the driver turns the steering wheel at the same speed (i.e., rotation speed) by applying the same amount of steering torque, for example, the direction in which the host vehicle travels will change more when the host vehicle is traveling at a relatively high speed than when the host vehicle is traveling at a relatively low speed. Therefore, the following problem arises when the change type determining process starts after the steering torque and/or the offset of the vehicle from the center of the lane exceeds the respective predetermined threshold value, as is the case with the system described in JP-A-2001-206237. For example, if it has been determined that the host vehicle is making a road change and the host vehicle is traveling faster than a predetermined speed, the host vehicle may veer out of the lane between the time that the lane departure preventing operation starts and the time that the driver actually becomes aware of the road change.
An example of when the host vehicle is traveling faster than a predetermined speed may be when the host vehicle is traveling in a passing lane next to a running lane. That is, with an assist system that starts operating based on a predetermined threshold value, as the system described in JP-A-2001-206237 does, the start timing of the operation may be late, such that the intended aim of the system is not able to be achieved. Therefore, the start timing of the operation of the assist system needs to be changed according to the type of lane that the host vehicle is traveling in.